1. Field of the Invention
Embodiments disclosed herein relate generally to filter screens. Particularly, embodiments disclosed herein relate to filter screens used in vibrating separators for wet or dry applications.
2. Background Art
Vibratory separators have long been used for the separation of both dry and wet materials, and are used in industries as varied as the chemical, food and beverage, powder coating, pharmaceutical, plastic, pulp and paper, ceramic, oilfield, and laundry industries. Vibratory separators, as used herein, generally refer to any type of separator or sifter used in the industrial processing of materials. Examples of materials and applications of industrial separators include metal powder, flour, sugar grinding, salt, steel shot, meat meal, sugar scalping, plastics, resin, fertilizer, petroleum coke, pharmaceuticals, wheat, soybean and oilseed, pellets and crumbles, and clay. Such separators may be circular or rectangular in cross section, and may include a vibration-generating device and resiliently mounted housings. Filter screens are fixed to the vibratory housings such that material fed to the vibrating filter screens may be screened. Various vibratory motions may be employed to work the material on the screen in the most advantageous manner. Frequently, discharge openings are provided both above the screening mechanism and below for retrieving the separated materials.
Some factors for selecting a particular vibratory separator include general material information, material characteristics, wet material data, material safety information, separator efficiency requirements, and desired use for the vibratory separator. For example, general material information may include the material to be screened, the temperature of the material, bulk density, specific gravity, and particle shape (spherical, fibrous, platelet, etc.). Materials may be characterized as granular, powder, abrasive, electrostatic, sticky, corrosive, free flowing, and agglomerates, among other characterizations. Key wet material data may include whether the material is viscous, greasy/oily, thixotropic, paste-like, sticky, or fatty. Furthermore, standard process data such as feed rate and minimum/maximum percentage of solids are important factors for selection of a vibratory separator. MSDS information, including numbers representing the severity of health, flammability and reactivity may be important depending on industry and application. Efficiency requirements vary by industry and application and are also important factors. Finally, those of ordinary skill in the art will appreciate that a vibratory separator may be used to scalp, dedust, or dewater, among other alternative uses.
In operation, a vibratory separator may be actuated to provide a flow of materials through the vibratory separator, such that solid particles are divided according to relative size. Thus, as the materials flow over a screen, larger particles exit the vibratory separator through a discharge outlet, while smaller particles exit through a secondary discharge area. The screen may include one or more filtering elements that may be manufactured from metals, plastics, cloth, and/or composites. Screens may be selected based on mesh size or micron size, among other sizing selection alternatives.
Over time, screens may be exposed to erosive and/or corrosive substances and operational conditions that degrade the screen effectiveness or efficiency of the filtering elements. Examples of operational conditions that may cause such an effect include typical actuation of the vibratory separator to impart movement in vertical and lateral directions. Over time, the vibratory motion, for example, in the vertical direction, may decrease the integrity of the screens due to structural damage, filtering element loosening, and the like. Such decreases in integrity may manifest as a slackening of the screen or parting of the screen from the frame, frame warpage or failure, or failure of the filtering element at the intersection with the frame. Further, screen failure may result from a broken screen, a screen tear, or bypass around a screen from improper sealing.
Screen failure may result in oversized particles entering the discharge underflow line of a vibratory separator. In wet screening of certain products, a maximum particle size may be important to manufacturing processes, and failure to screen to such a maximum size may lead to a large amount of final product being rejected or having to be reworked at a significant expense.
Accordingly, there exists a need for high strength filter screens for use in the separation of dry and wet materials.